There is a demand for manganese compounds that can serve as starting materials for obtaining lithium manganese composite oxides suitable as positive electrode materials for lithium secondary batteries. Such manganese compounds include manganese oxides, such as manganese dioxide obtained by electrolytic methods (electrolytic manganese dioxide, MnO2), and dimanganese trioxide (Mn2O3), trimanganese tetraoxide (Mn3O4) and manganese oxyhydroxide (MnOOH) obtained by chemical synthesis methods.
Of these manganese oxides, trimanganese tetraoxide and dimanganese trioxide have high theoretical density as calculated from their crystal structures. Therefore, trimanganese tetraoxide and dimanganese trioxide have high packing properties, and have become a subject of focus as manganese starting materials for obtaining lithium manganese composite oxide with excellent cell performance.
In the case of trimanganese tetraoxide, there has been reported a method of obtaining trimanganese tetraoxide by generating manganese hydroxide from a manganese solution under an ammonia-containing alkaline atmosphere, and then oxidizing the solution (see PTL 1, for example). Another method that has been reported is one wherein manganese ion, ammonia and hydrogen peroxide are combined in an aqueous alkali solution to obtain trimanganese tetraoxide (see PTL 2, for example).
Dimanganese trioxide obtained by heating electrolytic manganese dioxide at a high temperature is most commonly used in the industry, as a starting material for lithium manganese composite oxide (see PTLs 3-6). There has also been reported the use of dimanganese trioxide obtained by high-temperature heating of manganese carbonate while adjusting the oxygen concentration during firing (PTLs 7-8), and dimanganese trioxide obtained by firing trimanganese tetraoxide with a BET specific surface area of 10 m2/g to 80 m2/g (PTL 9), as starting materials for lithium manganese composite oxides.